EFFECT OF IRRIGATION WATER QUALITY AND WETTING AND DRYING CYCLES ON THE RELEASE OF SODIUM AND POTASSIUM IN TWO SOILS OF DIFFERENT ORDERS.

The study included two soil sites of different order (Inceptisols and Vertisols) within Nineveh Governorate, Iraq. Soil samples were taken from the surface depth (30 cm) naturally by means of columns. The experiment was carried out by adding two types of water (river water and well water) to each column with a volume equivalent to the pore size, and alternating wetting and drying were done for ten cycles, and the period between one cycle and another was 10 days. Soil samples were analyzed after the first cycle, the fifth cycle and the tenth cycle to find out the effect of the number of hydration cycles on the exchanged ions, the relative activity RA and the Gapone’s constant KG. The results indicated that the amount released from the exchanged sodium and potassium ions in vertisols was generally greater than the amount released in the soil of inceptisols when using both types of water, while the relative activity values of sodium were higher when wetting with well water except for the first cycle in the soil of inceptisols, while the relative activity of potassium in the two soils of the study, the values were higher when wetting with river water and for all cycles except the fifth cycle in inceptisols, while the Gapone’s constant for sodium in the two study soils had higher values, when wetting with river water in the first and fifth cycles, but in the tenth cycle the values were higher when wetting with well water, while the Gapone’s constant for potassium in the two study soils, the values were higher when wetting with well water and for all cycles except for the fifth cycle in inceptisols. The following kinetic equations were applied: Zero order equation, First order equation, Diffusion equation, Eluvich equation and Power function equation, the power function equation was the best equation that describes the process of release sodium and potassium ions in the study soil. [ABSTRACT FROM AUTHOR]